The present invention relates to a belt filter press for filtering a heavy liquid such as sludge into liquid filtrate and a solid filter cake, and in particular to an improved rotating roller over which the belts of the press pass to squeeze the liquid from the sludge.
Various constructions of continuously operating belt filter presses are known. In order to separate the solid particles from heavy sludge, the latter is brought between two continuously circulating screen belts, between which the liquid therein is drained and a filter cake is formed on the solid particles on progressively moving the belts together. The filter cake is automatically removed from the screen belts at a discharge point, for further processing. The screen belts are normally guided over rotary rollers and as a result of the reversal of the belts, a pressing action is exerted on the filter cake located between them, so that better draining is obtained.
The filter cake obtained can be used for various purposes. However, in many cases it constitutes a nonreusable waste product, which must be eliminated, e.g. burnt in some way.
As the moisture still present in the filter cake is generally disadvantageous for any further treatment, every effort is made to improve the belt filter presses in such a way that the filter cake obtained has a minimum water or moisture content. For this purpose, it is possible to feed the screen belts over further pressing zones. However, this involves an increase in the size of the machine and an extension of the drive means, which has a disadvantageous effect on costs, so that such a solution is generally unacceptable.
The object of the present invention is to improve the degree of drainage in belt filter presses. The problem is to improve the drainage level offered by such a press without making the machine larger or more complicated.
It is a specific object of the present invention to provide an improved roller by which increased pressure can be exerted on the belts and by which the filtrate can be drawn off and eliminated quickly and with greater efficiency. These objects as well as others will be seen from the foregoing disclosure.